Over the last decade NV centres have been demonstrated usefull for numerous applications from nanoscale magnetometry (Figure 1(a)) to quantum information processing (Figure1 (b)), through single-photon sources, nanophotonics, and nano-medicine. In order to improve the efficiency of NV centre based devices, it is crucial to precisely control their fabrication.
For instance, for the quantum information processing application the most challenging task is to create deterministic scalable net of coupled NVs. The most natural way to couple the implanted NVs is the magnetic dipolar interaction. Since the coupling strength decreases as inverse cubic distance between two NVs a high spatial resolution technique for precise N placement is required (distance should be less than 20 nm). Ion-implantation techniques are perfectly suitable to reach such resolutions. The advantage of this approach is a fine control of NV fabrication due to tunable parameters such as ion energy (to vary the implantation depth), size of holes in collimating masks (to minimize of the ion beam focused spot) and ion flux (change of number of NVs).
Using the i-FIB column, which is based on an Electron Cyclotron Resonance (ECR) source for the ions, 14N2 molecules were implanted at 30 keV energy by varying the dwell time of the beam. The kinetic energy of the ions corresponds to an implantation depth of 15 nm below the surface. Despite the surface proximity, spectral analysis showed that the spots consist of negatively-charged NV defects. Preliminary analysis based on the PL intensity level, the depth of the antibunching dip in the photon correlation record and GSD optical microscopy gave an evidence that 8-9 individual defects are dispersed inside each implanted spot within ∼100 nm (Figure 2). The ion-implanation resolution might be improved by the implementation of a beam collimation system, which is an essential point in order to reach ∼10 nm.
Figure 2 : PL image of one of the fabricated patterns with 9 of the implanted spots, which was implanted with the focused beam of 14N2 ions and during 1 ms of the dwell time. Each bright spot corresponds to approximately nine NV centers. The inset shows a higher resolution image of one of the implanted spots.
The advantage of the ECR ion source is its easiness to operate with different gases. For instance, by simple gas bottle replacement from nitrogen to xenon, the FIB source might be used to perform milling in a diamond. Therefore such structures as microlenses and pillars could then be created complementary to the nitrogen implantation. Moreover a combination of confocal microscope system with FIB column could allow us to fabricate a SIL all around a chosen NV center to maximize the efficiency of the light collection (Figure 3). It should be mentioned that due to the dual-beam configuration of the column (Focused Ion Beam is combined with Focused Electron Beam), all the process of diamond implantation and milling can be controlled in-situ.